A low background spontaneous fission detection system

Abstract A system for measuring very low spontaneous fission rates (appr. 1 event/month) is described. Small and thin samples placed onto mica are investigated. A fission event is determined by coincident registration of a fission fragment in a semiconductor detector and fission neutrons in a large liquid scintillator tank. Fission tracks in mica are used to confirm the existence of fission events observed by the counter coincidence. As background, zero events were found within two years. The results on the operation of the system during the past two years are presented in this paper.